The present invention relates in general to power modules containing high-power transistors for use in inverters for electric vehicles, and, more specifically, to substrate and connector pin configurations to improve space utilization and reduce signal interactions.
Electric vehicles, such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), and battery electric vehicles (BEVs), use inverter-driven electric machines to provide traction torque. A typical electric drive system may include a DC power source (such as a battery pack or a fuel cell) coupled by contactor switches to a variable voltage converter (VVC) to regulate a main bus voltage across a main DC linking capacitor. An inverter is connected between the main buses and a traction motor in order to convert the DC bus power to an AC voltage that is coupled to the windings of the motor to propel the vehicle.
The inverter includes transistor switching devices (such as insulated gate bipolar transistors, or IGBTs) connected in a bridge configuration with a plurality of phase legs. A typical configuration includes a three-phase motor driven by an inverter with three phase legs. An electronic controller turns the switches on and off in order to invert a DC voltage from the bus to an AC voltage applied to the motor. The inverter may pulse-width modulate the DC link voltage in order to deliver an approximation of a sinusoidal current output to drive the motor at a desired speed and torque. Pulse Width Modulation (PWM) control signals applied to the gates of the IGBTs turn them on and off as necessary so that the resulting current matches a desired current.
Because of the relatively high power (e.g., 100 kW) being handled by the inverter switching transistors, they are typically constructed as power modules which plug into sockets on a main circuit board containing a motor controller IC and other support circuits. Heat removal structures, such as a liquid-cooled cold plate, are typically disposed in contact with the power module(s) to handle the large amounts of heat that are generated. A typical module may include a DCB (direct copper bonded) substrate with one or more power transistor chips soldered onto a copper layer, a lead frame with multiple input/output pins, and an overmolded body encapsulating the module.
A power module may include just one switching element (e.g., an IGBT together with a freewheeling diode, a reverse-conducting or RC-IGBT, or a SiC MOSFET), which is referred to as a 1-in-1 power card. A power card may be single-side cooled or double-side cooled. A power module may also have a plurality of switching transistors, i.e., an N-in-1 power card. A 2-in-1 power card can be used to form a single phase leg of an inverter bridge. Power modules are also available with 4 or more switching transistors internally connected in a configuration that provides a plurality of phase legs, and may sometimes include redundant transistors connected in parallel when forming a phase leg.
The power module may typically have the shape of a flat, thin plate. Connector pins extending from the module include power terminals for the inputs and output(s) of the phase leg(s) and signal pins for the transistor control signals (i.e., gate signals) and various sensor signals. For example, many power modules have been provided with on-chip temperature sensors and/or current sensors.
In one type of conventional design, the power terminals and signal pins extend from one or more of the narrow sides or edges of the module. The terminals/pins can remain straight so that when plugged into a socket on a main circuit board, the module is oriented transverse to the main circuit board and both of the largest sides of the module are exposed for heat removal by a heat sink or cold plate. The terminals/pins can also be bent so that the module lays flat on the main circuit board. In any event, the relatively high voltage levels that may be present between different terminals/pins dictate a minimum spacing between adjacent terminals/pins. As the number of devices and the associated sensors increases, more terminals/pins are needed for the module and the required length of the sides of the module where the terminals/pins are arranged also increases. Consequently, the footprint on the main circuit board may be undesirably increased. This problem is especially significant when using a DCB substrate because the simplest and least expensive manner for forming the terminals/pins is for them to extend outward along the plane defined by the DCB substrate, which results in the terminals/pins all occupying a single layer.
The necessary chip size for any particular power capability has been shrinking as a result of developments in the field of power semiconductors which have achieved lower losses, higher current densities (e.g., SiC power devices), and reverse conducting capability (e.g., RCIGBT). However, arrangement of the signal pins in a single layer might limit the potential use of reduced chip size and further reductions of power card size, especially for N-in-1 power cards with N greater than 2.
Another consequence of having the signal pins arranged in one layer is that the power terminals are on the same layer with the signal pins. Therefore, the signal pins have been spaced from the power terminals so that the magnetic field generated by power terminals will not couple to the signal loops (i.e., so that there is no constructive or destructive interference with the signals being conducted on the signal pins). Thus, single layer modules employ pin spacing that avoids coupling from a power loop to a signal loop which could otherwise induce a gate current that inadvertently turns on one of the power devices, slows down the switching speed of the power devices, and/or interferes with the on-die sensors' signals. However, it would be advantageous to reduce the spacing without causing such coupling.